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Offline neilep

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Why Are Some Trees Evergreen ?
« on: 24/02/2012 12:43:58 »
Dearest Tree-ologists,

As a Sheepy I of course luff trees. Trees are my all time favourite large plant that ewe can build houses in.


As ewe know there are but just two types of tree.


Evergreen and Deciduous.

Look here are some Evergreen trees !




Some Everegreen trees hanging about....hmm...somethings seems weird !  ::)



And here is an Oaky deciduous !




Eric Will Shed His Leaves Later In The Year.... which is nice !



So, why so some trees hang on to their leaves all the year round and why do others....not ?


What's the advantages and disadvantages of both ?



Ta !


If ewe can let me know I will be most happy to absorb that knowledge !



hugs and shmishes



mwah mwah mwah !!



neil
One Two Tree
xxxxxxxxxxxx








 

Offline Don_1

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Re: Why Are Some Trees Evergreen ?
« Reply #1 on: 24/02/2012 14:20:38 »
 Why you decide you ask this treemendous kweschun? Perchance you are ever green with envy of those who are in the know but leaf it to others to ask before imparting their wisdom, for fear that the knowledge will be sapped from them. One of the root causes of botanists going barking mad or branching out into some other discipline.

Alright, so that was a corny thing to say. But I have given you previous warning, Mr Sheepy.

Sow So, what are the advantages of being evergreen? Well, for starters growing leaves is a pretty costly affair, so if you can hang on to them through the winter, you’ll be in a fine position to start photosynthesising as soon as spring comes around, ‘cause you’ll already have your leaves. What’s more, you can get on with growing straight away, rather than having to grow a whole new canopy first. But leaves in winter present some serious problems. They can freeze and act as giant sail, catching the wind and putting the tree at risk of being blown down. So the evergreens of the cooler temperate zones tend to have rather small cylindrical leaves. These do have some distinct advantage for those evergreen trees. They require less food (most of these trees are native to regions where the soil is poor), are resistant to very low temperatures and help to conserve water.

The deciduous trees have to grow a whole new canopy every spring. That requires a great deal of energy, but these trees do tend to live in far better soil. In fact, their own leaves, once fallen, help to enrich the soil. Their large leaves would become severely damaged by sub-zero temperatures, but large leaves capture more solar energy so they photosynthesise at a far greater rate than the needle like leaves of the evergreens. Discarding your leaves for the winter minimises the risk from damage by high winds and sub-zero temperates.

But evergreens are not restricted to the temperate zones. Many trees in the equatorial regions are considered to be evergreens. As they are not liable to experience the freezing temperatures that the temperate evergreens have to put up with, they can grow large leaves, just as the deciduous trees do. The difference here is that these trees do in fact shed their leaves, but not all at the same time. Where the deciduous trees shed all their leaves during the winter, these tropical trees will loose more of their leaf during the high summer. This is to reduce water loss through the leaves at a time of high temperatures, blistering sun and lower rain fall. But it is these trees which have the best of both worlds. Remaining evergreen throughout the year, they can photosynthesise continuously, where the trees, evergreen and deciduous, of the temperate zones must close down during the winter months. This continuous growth, enabled by rich soil, the forests’ own ability to produce good rainfall and year-round sun, has led to the largest living organisms on Earth.


A Sequoia being one of the largest organsims on Earth early today.

Pretty clever things these leaves and I have really only scratched the surface of their complexity. I think we should all hug a tree. If the order was given, I would, wood yew?
« Last Edit: 24/02/2012 14:22:33 by Don_1 »
 

Offline Geezer

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Re: Why Are Some Trees Evergreen ?
« Reply #2 on: 24/02/2012 16:31:58 »
And, too, as well, forby, just because they have needles and cones, they may not be "evergreen". The forests around here are mostly fir and pine, but there is a lot of larch mixed in. In the summer, the larches look pretty much like a fir tree, but they turn yellow in the fall and dump their needles.

The following link will fill you in on any minor details I may have overlooked.

http://www.mountainlarch.com/Mountain_Larch/Home.html
 

Offline neilep

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Re: Why Are Some Trees Evergreen ?
« Reply #3 on: 24/02/2012 18:00:13 »
Why you decide you ask this treemendous kweschun? Perchance you are ever green with envy of those who are in the know but leaf it to others to ask before imparting their wisdom, for fear that the knowledge will be sapped from them. One of the root causes of botanists going barking mad or branching out into some other discipline.

Alright, so that was a corny thing to say. But I have given you previous warning, Mr Sheepy.

Sow So, what are the advantages of being evergreen? Well, for starters growing leaves is a pretty costly affair, so if you can hang on to them through the winter, you’ll be in a fine position to start photosynthesising as soon as spring comes around, ‘cause you’ll already have your leaves. What’s more, you can get on with growing straight away, rather than having to grow a whole new canopy first. But leaves in winter present some serious problems. They can freeze and act as giant sail, catching the wind and putting the tree at risk of being blown down. So the evergreens of the cooler temperate zones tend to have rather small cylindrical leaves. These do have some distinct advantage for those evergreen trees. They require less food (most of these trees are native to regions where the soil is poor), are resistant to very low temperatures and help to conserve water.

The deciduous trees have to grow a whole new canopy every spring. That requires a great deal of energy, but these trees do tend to live in far better soil. In fact, their own leaves, once fallen, help to enrich the soil. Their large leaves would become severely damaged by sub-zero temperatures, but large leaves capture more solar energy so they photosynthesise at a far greater rate than the needle like leaves of the evergreens. Discarding your leaves for the winter minimises the risk from damage by high winds and sub-zero temperates.

But evergreens are not restricted to the temperate zones. Many trees in the equatorial regions are considered to be evergreens. As they are not liable to experience the freezing temperatures that the temperate evergreens have to put up with, they can grow large leaves, just as the deciduous trees do. The difference here is that these trees do in fact shed their leaves, but not all at the same time. Where the deciduous trees shed all their leaves during the winter, these tropical trees will loose more of their leaf during the high summer. This is to reduce water loss through the leaves at a time of high temperatures, blistering sun and lower rain fall. But it is these trees which have the best of both worlds. Remaining evergreen throughout the year, they can photosynthesise continuously, where the trees, evergreen and deciduous, of the temperate zones must close down during the winter months. This continuous growth, enabled by rich soil, the forests’ own ability to produce good rainfall and year-round sun, has led to the largest living organisms on Earth.


A Sequoia being one of the largest organsims on Earth early today.

Pretty clever things these leaves and I have really only scratched the surface of their complexity. I think we should all hug a tree. If the order was given, I would, wood yew?


THANK YOU VERY MUCH Don for the wonderful information. Wow...That Sequoia !....ewe know.......I'm having it delivered next Tuesday !...

Did I perchance Ce-dar punning threads influence infiltrating the first few lines of your response  ?... I figured it wood  have been a joak !...But then I thought not... everything was Sequoa-enced so welm. *groan*...I just can't do this ash well as Yew lot !
 

Offline neilep

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Re: Why Are Some Trees Evergreen ?
« Reply #4 on: 24/02/2012 18:03:23 »
And, too, as well, forby, just because they have needles and cones, they may not be "evergreen". The forests around here are mostly fir and pine, but there is a lot of larch mixed in. In the summer, the larches look pretty much like a fir tree, but they turn yellow in the fall and dump their needles.

The following link will fill you in on any minor details I may have overlooked.

http://www.mountainlarch.com/Mountain_Larch/Home.html

Excellent stuff !..TA very much Dr Geeza !...thank you for the link.


So could there be a half way house between Evergreen and deciduous ?
 

Offline Geezer

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Re: Why Are Some Trees Evergreen ?
« Reply #5 on: 25/02/2012 10:15:59 »

So could there be a half way house between Evergreen and deciduous ?


Beats me! I think even the evergreens are not quite as green as they like to make out. At certain times, a fair amount of their needles turn brown and fall off, and in the Spring, particularly with fir trees, the new growth is a really brilliant light green.

I'm sure Prof Don will be able to clue us in on this stuff.
 

Offline Don_1

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Re: Why Are Some Trees Evergreen ?
« Reply #6 on: 27/02/2012 11:40:00 »
PROF DON???? Ah of course! You mean profiteroles Don. A reflection on my love of choux pastry, dairy products and chocolate.

So, I see you have revealed the scandalous nature of those fraudulent firs, posing as ‘evergreens’, then dropping their needles all over the place.

I don’t think you could say there is a halfway house between deciduous and evergreen trees. The fact is that even the evergreens drop their leaves, or needles, but retention of the needles can be for periods of 2 – 5 years and new needles, though mainly being ‘born’ in the spring, are produced throughout the growing season. They will drop off at almost any time. I think studies on the needle retention and density of fir trees found some weak correlation between weather, tree age and other factors, but no definite pattern which could be used as a standard model.

The term ‘evergreen’ refers not to leaf life, but to leaf density. Deciduous trees have a definite cycle of high leaf density and no leaf, while the evergreens have periods of high and low leaf density, but never drop all their leaves at one time.

But there are some trees which you might call extreme evergreens, which have a leaf life which is far beyond that of the conifers of the temperate zones. One such tree is the Andean  Araucaria araucana or Monkey Puzzle tree, which has a leaf life of 24 years (average) and has been suggested that the leaves could last as long as 40 years. Other trees of the Andean forests are also thought to have comparatively long leaf life.
 

Offline Geezer

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Re: Why Are Some Trees Evergreen ?
« Reply #7 on: 27/02/2012 18:30:05 »
Well, I dunno, but that seemed like a professorial response to me. Are yew sure you are not actually a prof of biology at some uni?
 

Offline Don_1

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Re: Why Are Some Trees Evergreen ?
« Reply #8 on: 28/02/2012 18:11:03 »
Well, I dunno, but that seemed like a professorial response to me. Are yew sure you are not actually a prof of biology at some uni?

OK, so I've been sussed. I might as well come clean, I am in fact a PhD ( fffd ) with a doctorate in bottomy, no, I didn't spell that wrong.
 

Offline wolfekeeper

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Re: Why Are Some Trees Evergreen ?
« Reply #9 on: 29/02/2012 17:45:36 »
FWIW evergreens have to have antifreeze in the needles to prevent them freezing solid, so they use things like sugars to depress the freezing point. It obviously takes energy to make the sugars though.
 

Offline CliffordK

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Re: Why Are Some Trees Evergreen ?
« Reply #10 on: 22/03/2012 12:16:36 »
But leaves in winter present some serious problems. They can freeze and act as giant sail, catching the wind and putting the tree at risk of being blown down.
We just went through a March snowstorm, and I lost a few branches off of my trees...

But, it got me thinking. 

The shape of the tree may also be a major factor. 

The hardwoods tend to have multiple upward branches, essentially forming a ball shape.  They would be seriously at risk of collapse if they had a severe snowstorm with a full canopy of leaves.  Even so, an ice or snow storm can weigh down bare branches in the winter, and still cause some damage.

The conifers, on the other hand have a centeral trunk with horizontal branches...  that get weighed down to give them a conical shape.  And thus they are better suited to shedding snow and ice.  Nonetheless, if a horizontal branch cannot bend enough, it will break, and I lost numerous 4" to 6" branches off of my trees with this spring snowstorm.  However, having a straight vertical trunk lowers the risk of the snow putting the trunk off balance and shattering the main trunk.
 

Offline Airthumbs

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Re: Why Are Some Trees Evergreen ?
« Reply #11 on: 23/03/2012 02:39:37 »
Ilix Aquafolium, or Holly, does not have pine leaves and can be found growing alongside deciduous trees.  One advantage that many evergreens have over deciduous trees is that they can tolerate more extreme environmental conditions. 

Deciduous trees in equatorial regions have no seasons, they do not shed there leaves as there is no large variable in temperature year round, this is also why the timber has no growth rings and why the wood is so valuable, wood with no growth rings is much stronger.  Most of these deciduous tropical trees are not drought tolerant whereas evergreens are more resistant.  This is a big problem for our rain forests as there have been successive droughts over the past decade causing massive die back.

Another interesting fact you might not know about pines and most coniferous species is that they contain pesticide in the leaves.  They do constantly loose their leaves hence the brown mat of dead pine needles you see on the forest floor.  However not much else grows under these canopies due to the pesticidal effects.

I think basically to sum it up, evolution in response to changing climate is mainly what is responsible for the divergence of trees species.

This website is quite interesting as it supposedly follows the historical evolution of trees.... http://www.bomengids.nl/uk/tree-evolution.html
« Last Edit: 23/03/2012 02:43:40 by Airthumbs »
 

Offline Geezer

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Re: Why Are Some Trees Evergreen ?
« Reply #12 on: 23/03/2012 04:12:55 »

The hardwoods tend to have multiple upward branches, essentially forming a ball shape.  They would be seriously at risk of collapse if they had a severe snowstorm with a full canopy of leaves. 
 

That's exactly what happened last October in the Northeast US. There was a very early snowfall while most of the trees still had their leaves. Mrs G was visiting our daughter in NJ at the time. The power was out for the entire week she was there!
 
Evergreens will usually do much better in an ice storm, but only if they have symmetrical foliage. If they are crowded, the foliage can be very asymmetrical, so the weight of the ice starts to bend the trunk. Once that happens the buildup of ice accelerates, and it's just a matter of time until the trunk snaps. It's amazing just how much they will bend before they snap.
 
Ice storms are really strange. Almost total silence occasionally interrupted by the explosive sound of massive tree trunks snapping. 
 

Offline Airthumbs

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Re: Why Are Some Trees Evergreen ?
« Reply #13 on: 23/03/2012 20:40:16 »
Evergreens will usually do much better in an ice storm, but only if they have symmetrical foliage. If they are crowded, the foliage can be very asymmetrical, so the weight of the ice starts to bend the trunk. Once that happens the buildup of ice accelerates, and it's just a matter of time until the trunk snaps. It's amazing just how much they will bend before they snap.
 

The crowded trees will also be Etoliated, meaning they will suffer from weak stems that are tall and thin.  This is an indication that the trees need to be thinned.  In a way it is a good thing that the ice storms do some thinning for you although it sounds scary!!
 

Offline CliffordK

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Re: Why Are Some Trees Evergreen ?
« Reply #14 on: 23/03/2012 21:44:52 »
Actually, what I've noticed is that the isolated fir trees are the ones with thick lower branches that are susceptible to breaking under the stress of snow, and are far more dangerous if they should fall on one's head.

The more densely packed trees tend to have the lower branches die out sooner, and thus they are smaller and fewer branches. 

For timber, the fewer low branches, the better.  Some of my trees with 6" knots would make pretty poor wood, although almost big enough to cut a 2x4 out the branches if they only were straighter.  So the trees need at least moderate density to grow good wood.  Obviously, as the trees grow, they may reach a point where thinning is appropriate.

Clearcutting, of course, is controversial.  It allows light down to the forest floor which is good for young trees, but it does leave the hillsides bare which can bring other problems including erosion, and later risk of fires with thick undergrowth.
 

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Re: Why Are Some Trees Evergreen ?
« Reply #15 on: 24/03/2012 07:08:43 »
Snow perhaps, but I'm talking about an ice storm. The trees at the edge of a crowded cluster have a lot of foliage on the outside only. A coating of ice builds up on the foliage, and the whole tree starts to bend. Once it starts to bend, even more ice coats the foliage and the entire trunk forms an arc. The process continues until the trunk pops.
 

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Re: Why Are Some Trees Evergreen ?
« Reply #15 on: 24/03/2012 07:08:43 »

 

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